The Phone Guy is Freddy Aside from you and the four animatronics the only other character in the game is someone referred to as Phone Guy. He calls you each night at the beginning of the level to offer advice on how to stay alive.
Except that he really doesn't. His advice is usually wrong and he claims that the player is really in no danger half the time. He even tells you to leave the room, which would probably be an instant kill. Even on the fourth night when it sounds as if the animatronics are attacking him he exhibits no real panic. The theory goes that Phone Guy is actually the animatronic Freddy Fazbear himself using the same voice box that lets him sing at shows during the day.
On the other hand, there is that weird fifth message...
Phone Guy is a Creation of the Animatronics One the last night the final message is strange, haunting, garbled, and very disturbing. However, it has been translated...
"(Omitted: it is lamentable that mass agricultural development) is not speeded by fuller use of your marvelous mechanisms. Would it not be easily possible to employ some of them in quick laboratory experiments to indicate the influence of various types of fertilizers on plant growth?" "You are right. Countless uses of (omitted: Bose instruments) will be made by future generations. The scientist seldom knows contemporaneous reward; it is enough to possess the joy of creati- (omitted: -ve service.)"
This is a passage from Paramahansa Yogananda's famous Autobiography of a Yogi, one of the books that brought Eastern spirituality to the West. It deals very much with the attainment of God-realization, and was a favorite of tech wizard Steve Jobs. The use of the passage hints that the work of the animatronics are actually experiments in converting biological life into their own form, experiments that result in Phone Guy.
This story continues on the next page.